Device for coupling a pair of rods

ABSTRACT

A coupling is mounted between a valve steam of a valve and a rod of a valve actuator. The rod includes an extension having a piston member at the end thereof which is received within a cylinder member mounted on the end of the valve stem. The extension and piston member thereof define with the cylinder member a chamber within the cylinder member. Force can be transmitted from the rod to the stem by full insertion of the piston member within the cylinder member. Hydraulic fluid under pressure from an accumulator secured to the cylinder member is in communication with the chamber to limit the force transmitted from the rod to the stem when the relative position of the rod with respect to the stem causes the piston member to be located intermediate of the cylinder member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a device for coupling a pair of rod elementsand, more specifically, to such a device which can be utilized to limitthe amount of force applied to a stem of a valve during backseating whenthe rod of a valve actuator acts on the valve stem to open the valve.

2. Description of the Prior Art

There have heretofore been utilized a number of means for opening andclosing large valves in the feedwater and steam systems of nuclear powerplants. One such means which is frequently used is a valve actuatorwhich incorporates a hydraulic cylinder and a gas accumulator. Hydraulicoil is directed to a piston within the hydraulic cylinder to open thevalve in opposition to a precharged source of high pressure gas in anaccumulator which gas acts on the other side of the piston. The highpressure gas maintained in the accumulator is of a sufficient quantityand pressure to act on the piston to rapidly close the valve when thehydraulic pressure is relieved. Some valve configurations require ahydraulic pressure which is significantly higher than that of the highpressure gas to provide enough force to initially lift the closuremember from its seat. Employing the hydraulic pressure at such a highlevel could result in backseating damage if some means were not utilizedto limit the force during backseating.

In other valve configurations where such a large force is not requiredto lift the closure member from the seat, pressure limiting means, suchas a hydraulic accumulator, or a relief valve, on the hydraulic systemwhich provides the hydraulic pressure for opening the valve, may be setat a level to properly backseat the valve when the piston is in anupward position. The resulting force acting on the stem, the differencebetween the hydraulic force upward and the gas force downward, ismaintained to ensure proper backseating without damaging the valve.However, should a leak in or a rupture of the accumulator occur, theforce generated by the hydraulic oil would no longer be opposed by thehigh pressure gas. Were this force to be transmitted to the backseat ofthe valve through the stem, permanent valve damage might occur. Althoughit is less likely to occur, the same detrimental results might beobtained with failure of the hydraulic pressure limiting means.

A concern for and a consideration of the amount of force applied to avalve during backseating has also affected the operation of other formsof valve actuators. Although they are not capable of closing this typeof large valve as rapidly as can the accumulator described hereinabove,electric motor operators are frequently employed for valve operation innuclear power plant systems. To close a valve with an electrical motoroperator, a remote signal is sent to the motor to cause gear rotation inone direction to lower the rod. The motor gearing includes a torquelimit switch which is contacted during a predetermined torque conditionwithin the gearing so that when the rod has acted on the stem to fullyseat the valve, motor power is discontinued by the torque limit switch.Motor operation is, therefore, automatically stopped when the valve isfully closed. It would seem that a similar torque limit switch could beemployed in the motor gearing when the valve is opened. The motor wouldagain stop when the valve is backseated as an increase in torque wouldagain turn off the electrical motor. However, the level at which such atorque limit switch would be set to prevent damage during backseatingwould limit the torque throughout operation of the electrical motoroperator while opening the valve. But it is often found that asignificantly higher torque is needed simply to initially open thevalve. A torque limit switch with such a setting would, therefore,prevent the valve from being opened by disconnecting the motor prior toany upward movement of the stem. Consequently, it is presently thepractice in the operation of the electrical motor operator duringopening of the valve to provide a position limit switch for stopping themotor just prior to backseating of the valve. A handwheel is providedfor manually applying the proper torque to fully backseat the valve.

Last, but by no means least, there exist valve actuators which areoperated by hydraulic oil which acts on both sides of a piston toposition the valve. The use of hydraulic oil pressure to open the valve,without a controlled pressure on the other side of the piston inopposition thereto, has generally produced forces which areunsatisfactory for backseating the valve. Consequently, valves operatedby a hydraulic actuator have not heretofore been provided with anysimple, automatic means for backseating.

To provide some control of the forces being transmitted to a valve by anactuator during backseating, there has heretofore been disclosed acoupling of the type included in U.S. patent application Ser. No.663,786, filed on Mar. 4, 1976 by Timothy Edward Kunkle and assigned tothe assignee of this application. These couplings basically utilize aspring member to bias a pair of lost motion fittings mounted on the endsof the rod and the stem. Although these prior art devices can beproperly employed for this purpose, the basic design employed requiresone or more Belleville springs which are generally expensive to provideand lack a desired flexibility since specific springs may be requiredfor each specific valve configuration.

SUMMARY OF THE INVENTION

It is, therefore, an object of this invention to provide means forapplying an adequate but limited force to a valve stem by a valveactuator while ensuring proper backseating of the valve without anydamage thereto.

It is another object of the invention to provide a device for couplingthe valve stem and the rod actuator which utilizes a pressurized fluidto provide the desired force required for backseating.

It is a further object to provide a device of the type described whichcan be utilized on different valve configurations while still beingsimple to operate and inexpensive to provide.

These and other objects of the invention are provided by the preferredembodiment thereof in the form of a device for operably coupling a firstrod to a second rod having a common axis and being capable of movementalong the axis for transmitting force therebetween. The device includesan extension of the first rod which has an intermediate portion with anexterior surface which is parallel with the axis and an end portionextending radially from the exterior surface to define a piston member.A cylinder member is mounted at the end of the second rod and includes acylindrical wall that extends by the piston member for sliding, sealedcontact therebetween and has an end thereof remote from the second rodwhich includes an opening therethrough. The intermediate portion of theextension is received within the opening for sliding, sealed contactbetween the exterior surface and an interior surface of the opening. Theextension of the first rod and the cylinder member have mating surfacesthereon which are transverse to the axis for engagement therebetween toestablish a maximum axial distance between the rods. A chamber withinthe cylinder member is defined by the cylindrical wall, the end of thecylinder, the exterior surface and a first side of the piston member.The piston member has a second side thereof which is capable of engaginga contact surface relative to the end of the second rod to establish aminimum axial distance between the rods. An accumulator is mounted tothe cylinder member with an exterior thereof communicating with thechamber. The accumulator includes gas at a precharged pressure whichacts on hydraulic fluid therein which communicates with and fills thechamber. The hydraulic fluid in the chamber biases the first rod towardthe second rod and for limiting the tensile force being transmitted fromthe first rod to the second rod when a relative distance therebetween isless than the maximum axial distance and greater than the minimum axialdistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional side view of the preferred device for coupling arod and a stem including various features of the invention and shown ina position where there is a minimum axial distance between the rod andstem.

FIG. 2 is a fragmentary, sectional view of the coupling as shown in FIG.1 showing the relative position of the rod and the stem when the valveis being backseated.

FIG. 3 is a view like that of FIG. 2 with the rod and stem in a relativeposition with a maximum axial distance therebetween.

DESCRIPTION OF THE INVENTION

As seen in FIG. 1, the preferred device 10 for coupling a rod 12 of avalve actuator (not shown) to a valve stem 14, which is also a rod likemember, of a valve (not shown) is disposed therebetween in generalalignment with an axis 16 which is common to both the rod 12 and thestem 14. It will be seen that when explaining the device 10 generalreference will be made to portions thereof relating to the rod 12 or thestem 14. However, the device 10 and its components may be reversed inposition relative to the rod 12 and the stem 14 without altering itsfunction so that the invention is not limited to the particulararrangement shown.

In the preferred embodiment, the rod 12 includes an extension 18 thereofwhich is threadedly mounted thereon (as shown at 20). An intermediateportion 22 of the extension 18 includes an exterior surface 24 which isparallel with the axis 16. Although in the preferred embodiment theintermediate portion 22 is cylindrical in shape, it will be seen thatany portion having a uniform cross section along its length might beprovided if proper sealing (as will be discussed later) can be providedtherefor.

The extension 18 further includes an end portion in the form of a pistonmember 26 which extends radially from the surface 24 to have a largerdiameter than does the intermediate portion 22.

The stem 14 is provided with an end fitting 28 which is threadedlyreceived on the end 30 of the stem 14. Additionally, a cylinder member34 is mounted relative the end 30 of the stem 14 by including a cylinderbody 36 and a coupling ring 38. The coupling ring 38 and cylinder body36 are joined at threads 40 and entrap the end fitting 28 of the stem 14as a radial portion 42 of the coupling ring 38 closely encircles thestem 14. General contact between the end fitting 28 and the radialportion 42 of the coupling ring 38 is made at 44. Contact at 44, it willbe seen, will be maintained throughout valve operation and thetransmittal of force between the rod 12 and the stem 14 but radialsliding contact between the end fitting 28 and the coupling ring 38 at44 will accommodate alignment of the rod 12 and the stem 14 throughoutvalve operation. The cylinder body 36 of the cylinder member 34 includesa cylindrical wall portion 46 adjacent to and extending by the outerperiphery of the piston member 26. Accordingly, sliding contact isprovided between the periphery of the piston member 26 and thecylindrical wall portion 46 and a sealing ring 48 is mountedtherebetween.

The cylinder body 36 further includes an end 50 which has an opening 52therethrough. The intermediate portion 22 of the extension 18 isreceived within the opening 52 for sliding contact between the interiorsurface of the opening 52 and the exterior surface 24. Again, a sealingring 54, similar to sealing ring 48, is provided therebetween.

Accordingly, the exterior surface 24, a first side 56 of the pistonmember 26, the interior surface of the cylindrical wall portion 46 andthe end 50 of the cylinder member 14 define a chamber 58 which is sealedand capable of changing volume as the axial distance between the rod 12and the stem 14 is altered. To employ the chamber 58 to control theforce being transmitted from the rod 12 to the stem 14, a fluidaccumulator 60 is provided.

The fluid accumulator 60 is rigidly mounted to the cylinder member 34 bypiping 80 at a passage 82 which communicates with the chamber 58. Theaccumulator 60 is in the preferred embodiment a bladder-type in whichhydraulic oil is in the interior 84 and freely communicates with thechamber 58. Gas at a precharged pressure is provided the accumulator 60through a fitting 86 at the lower end thereof to act on the other sideof the bladder 88. As a result, the hydraulic oil acts as a pressurizedfluid within the chamber 58 for preloading the device 10 as will beexplained in detail hereinbelow.

As has thus far been explained, the preferred device 10 for coupling therod 12 and the stem 14 includes a means for limiting the tensile forcetransmitted between the rod 12 and the stem 14 when the axial distancetherebetween is such that the pressurized fluid in the chamber 58produces biasing between the rod and stem. However, a full explanationof the operation of the device 10 during opening and closing of a valveis in order for a better understanding of how it will function. Duringclosing of the valve in this preferred embodiment, the rod 12 will movedownward to transmit force to the stem 14. A curved second side 62 ofthe piston member 26 of the extension 18 will make contact with analignment surface 64 of the end fitting 28. Therefore, as seen in FIG.1, the distance between the rod 12 and the end 30 of the stem 14 duringclosing is shown at A and this distance is the minimum axial distancewhich can be obtained between the rod and stem when the device 10 isbeing utilized. The second side 62 is generally free to make slidingcontact with the alignment surface 64 of the end fitting 28 to insureproper alignment between the rod 12 and the stem 14 when compressiveforce is being applied therebetween. This alignment is made possible, asmentioned above, by the sliding contact which may occur between the endfitting 28 and the coupling ring 38 at the surfaces at 44.

During opening operation of the valve, forces acting on the rod 12 andstem 14 vary, depending on the valve position during opening.Accordingly, the relative positioning of the elements at the coupling 10is determined by the valve position and these forces. When the valve isinitially opened (being removed from its seat), a great deal of force isapplied to the rod 12 which is resisted at the stem 14 to cause theirrelative positions to be that which is shown in FIG. 3. This will beexplained in detail hereinbelow. However, once the valve is opened (whenit has been obviously removed from its seat), there are no appreciableflow forces applied to the valve closure member. As a result, thepressurized fluid within chamber 58 is capable of applying a force tothe rod 12 and the stem 14 which will fully overcome the resistance tomovement by the closure member so that they will return to theirrelative positions to be maintained at the minimum distance A as shownin FIG. 1.

However, as seen in FIG. 2, when the valve is backseated, the generalspacing between the valve and the actuator is such that the stem 14 willbe restricted in its upward movement. Further upward movement of theactuator causes the rod 12 to come to rest within the actuator where itwill be displaced from the end 30 of the stem 14 to an axial distance asshown at B. In this position, the pressurized fluid within the chamber58 acts on the piston member 26 and the cylinder member 34 to determinethe level of force being transmitted from the rod 12 to the stem 14.During the initial set up of the actuator-valve configuration thespacing of the various elements of the actuator and the valve isdetermined to insure that this general position is obtained duringbackseating while the rod 12 is being held upwardly against a stop inthe actuator.

However, there is a condition which has not yet been discussed which isof significance during initial opening of the valve. When a large valveis fully seated in a flow line, the liquid in the line createssignificant force on the closure member and the initial force requiredto remove the closure member from the seated position is significantlylarger than the force desired for backseating as described above.Accordingly, in some configurations, force being applied to unseat avalve would attempt to displace the rod from the stem and greatlydecrease the volume of the chamber 58. However, since there is noobjection to transmitting these higher forces between the rod 12 and thestem 14 except during a backseated condition, it is expected in thissituation that the first side 56 of the piston member 26 and theinterior surface of the end 50 of the cylinder member 34 will be forcedinto direct contact as seen at 66 in FIG. 3.

As seen in FIG. 2, these surfaces are generally perpendicular to theaxis 16 but are not caused to make contact when the valve is backseated.However, during initial opening of the valve, again referring to FIG. 3,the force transmitted between the rod 12 and the stem 14 issignificantly higher than the resistance afforded by the pressurizedfluid within the chamber 58 so that the rod 12 will be further displacedfrom the stem 14 to bring the first side 56 and the end 50 into contact.The abutting contact thus provided allows force applied to the rod 12 tobe directly transmitted to the stem 14 for proper unseating of thevalve. It can be seen that in this condition the volume of chamber 58 isat a minimum but free communication with the accumulator 60 prevents anexcessive build up of pressure by the pressurized fluid. Accordingly,when these surfaces are engaged the distance between the second side 62of the piston member 26 and the end 30 of the rod 12 is shown at C andthis distance is the maximum axial distance that can be establishedbetween the rod and the stem during valve operation.

As a result, if the distance between the rod 12 and the stem 14 isgreater than the minimum axial distance A and is less than the maximumaxial distance C the force being transmitted between the rod 12 and thestem 14 is determined by the pressure of the pressurized fluid operatingwithin the chamber 58.

Although the device 10 might be utilized for any type of valveindependent of size, it is presently being considered for globe valvesand gate valves ranging from 6 inches to 28 inches. However, it would behelpful to present some dimensions and quantities expected for a typicalvalve configuration. It has, for example, been determined that for a 16inch gate valve the desired backseating force could range between 11,000and 12,000 pounds. To provide this desired force, a first side of thepiston member might be designed to include a surface area of about 5square inches. By precharging the accumulator with gas to a level ofabout 2,000 p.s.i., it can be seen that the decrease in the volume ofthe chamber during backseating will cause the volume of the gas to bedecreased to raise the pressure to a level of about 2,200 to 2,400p.s.i. The system would work satisfactorily if the environmentaltemperature at the installation were to be quite high causing theprecharged gas to reach a level of about 3,000 p.s.i. Obviously, thiswould increase the backseating force but this higher force would bewithin the design parameters of the valve configuration.

A typical hydraulic system in an actuator being used to operate a 16inch gate valve would be expected to operate at a hydraulic pressure ashigh as 4,500 p.s.i. This level of pressure is sufficient to create anopening force (that needed to lift the gate initially off the seat) inthe range of 130,000 to 140,000 pounds of force. With this level offorce being transmitted from the rod to the stem, the mating surfaceswithin the device would be engaged for full transmission of the forcebetween the rod and the stem in the manner described hereinabove.

As thus explained, the preferred embodiment of the invention enables therod to transfer large forces to the stem but controls the force which isbeing transferred to the stem during backseating of the valve. Theembodiment shown might obviously be altered and still be seen to fallwithin the scope of the invention. For example, although in thepreferred embodiment the piston member and the cylinder member have acircular cross section, it could be seen that any uniform cross sectioncould be utilized although it is expected that sealing can be moreeasily provided with the design shown in the preferred embodiment.Additionally, while the extension is shown to be threadedly receivedwithin the rod, the extension might be integrally formed therewith tocause the intermediate portion to actually be a portion of the rodproper. Similarly, various configurations might be utilized for couplingthe shaft to the cylinder member and one alternative might include arigid attachment thereto if it is determined that the alignment problemmentioned hereinabove is not significant. Further, while the preferredembodiment utilizes the first side of the piston member and the end ofthe cylinder member for direct contact during initial opening of thevalve, other "mating surfaces" may be provided to accomplish the samedirect transfer of force when the volume of the chamber is decreasedbeyond that desirable for backseating. Clearly, other embodiments of thedevice taught herein could be employed while remaining within the scopeof the present invention.

We claim:
 1. A device for operably coupling a first rod to a second rodhaving a common axis and being capable of movement along said axis fortransmitting force therebetween, said device comprising:an extension ofsaid first rod having an intermediate portion with an exterior surfacewhich is parallel with said axis and an end portion extending radiallyfrom said exterior surface to define a piston member; a cylinder membermounted at an end of said second rod and including a cylindrical wallthat extends by said piston member for sliding, sealed contacttherebetween, said cylinder member having an end thereof remote fromsaid second rod which includes an opening therethrough; saidintermediate portion of said extension being received within saidopening for sliding, sealed contact between said exterior surface and aninterior surface of said opening; said extension of said first rod andsaid cylinder member having mating surfaces thereon transverse to saidaxis for engagement therebetween to establish a maximum axial distancebetween said first rod and said second rod; a chamber within saidcylinder member defined by said cylindrical wall, said end of saidcylinder member, said exterior surface and a first side of said pistonmember; said piston member having a second side capable of engaging acontacting surface on structure within the cylinder member located at apredetermined distance from said end of said second rod to establish aminimum axial distance between said first rod and said second rod; anaccumulator connected to said cylinder member with an interior thereofcommunicating with said chamber; said accumulator including gas at aprecharged pressure acting on hydraulic fluid therein which said fluidcommunicates with and fills said chamber; and said hydraulic fluid insaid chamber biasing said first rod toward said second rod and limitingtensile force being transmitted from said first rod to said second rodwhen a relative distance therebetween is less than said maximum axialdistance and greater than said minimum axial distance.
 2. A device asset forth in claim 1, wherein said accumulator includes a bladderelement between said hydraulic fluid and said gas at a prechargedpressure.